Magnetic transfer method refers to all action related to the movement of particles by means of magnetism, such as assorting, collecting, transferring, mixing and dosing within a solution or from one solution to another.
Particles, micro particles or magnetic particles refer to all such small particles that have their diameter in the range of micrometers, and that can be moved by means of magnetism. There are various known particles that are transferable with a magnet and also applications, where they are used, greatly vary. For example, particles used in microbiology usually have a size of 0.01-100 μm, most commonly 0.05-10 μm. Such known particles are, for example, particles containing ferromagnetic, paramagnetic or supra-magnetic material. Particles can also be magnetic themselves, in which case they can be moved by means of any ferromagnetic object.
In a device intended for to treat micro particles, there is a unit exploiting magnetism that is hereinafter referred to as a magnet. It can be a permanent magnet or an electrical magnet attracting particles, such as ferromagnetic, paramagnetic or super-paramagnetic particles, or a ferromagnetic object that is not magnetic itself, but still attracts magnetic particles.
A magnet is usually preferably a rounded bar magnet. It can also be a bar of another shape. However, a magnet does not need to be a bar at all. It can also be short and broad or an object of any shape. A magnet can also consist of one or more objects, such as magnets or ferromagnetic objects. The magnet can also be connected to objects consisting of non-ferromagnetic material.
There has to be a shield covering the magnet, protecting the magnet from various harmful conditions and enabling the treatment of micro particles, such as binding and release. The structure of the shield may greatly vary for it can be, for example, a thin membrane consisting of flexible or stretchy material or even a cup consisting of rigid plastic.
Micro particles are commonly used as a solid phase for binding various biological components, such as nucleic acids, proteins, toxins, cell organelles, bacteria or cells. For example, specific antibodies, oligonucleotides, polypeptides and lectins can be immobilized on the surface of micro particles. For example, enzymes can be immobilized on the surface of micro particles, whereupon the treatment and further use of the enzymes is efficient. Most of the so called magnetic nanoparticles (<50 nm) are not suitable to be treated with regular permanent magnets or electrical magnets, but require the use of an especially strong magnetic gradient, as described in EP 0842704 (Miltenyi Biotec). Magnetic particles, such as micro particles that have a diameter of about 0.1 μm or more, can usually be treated with regular permanent or electrical magnets. The viscosity of the solution can also considerably hamper the picking of the particles. The particles to be picked may originally be suspended in the solution, where a substance is desired to be bound, or say cells on the surface of the micro particles. It is of particular importance to be able to use large initial volumes in applications, where components are desired to be isolated for analysis. For example, efficient enrichment of pathological bacteria from a large sample volume to a little one is critical, because it has an effect on the sensitivity and time needed for analysis of a direct assay. At present there is no way sufficient enough to perform enrichment from a large volume to a little volume by means of micro particles. It would be preferable that a performance as described above would be as simple and efficient as possible.